1. Field of the Invention
The present invention relates to a wireless access communication system, and more particularly to a method for controlling a sleep mode in a wireless access communication system.
2. Description of the Related Art
In a conventional cellular network [e.g. a Code Division Multiplex Access (hereinafter, referred to as a CDMA) network, a Global System for Mobile Communication (hereinafter, referred to as a GSM) network, etc.], a slotted paging method is used for achieving a sleep mode. That is, when terminals operating in the conventional cellular network are not in an active mode, the terminals operate in a sleep mode, in which power consumption is reduced. The terminals periodically awake from the sleep mode to determine if messages have been received. The terminals are shifted to the active mode only when messages have arrived; otherwise, the terminals re-enter the sleep mode.
In the slotted paging method, since a paging slot, which in monitored by the terminal itself, is predefined between a base station and the terminal, each terminal has only to awake at the appointed paging slot in order to check its own paging message. For instance, a paging slot is defined for each terminal in a CDMA system, and a paging group is defined for each group of terminals in a GSM system. Accordingly, CDMA and GSM terminals have only to awake during the predetermined time periods. The predetermined time periods are fixed values specified by a system, and thus are easily realized and managed in the system.
However, in a wireless access communication system (also known as a 4th generation communication system) the supports high speed services, it is difficult to control a sleep mode. The reason for the difficulty in control is that in an IEEE 802.16e communication system, which additionally considers mobility of a subscriber terminal as compared with an IEEE 802.16a communication system, a sleep mode has a sleep interval that is increased according to an exponential power of 2 of an initial sleep interval (or twice as large as a previous sleep interval). It is not simple process to manage a sleep mode starting point of time, a sleep interval, and an awaking point of time for each of a plurality of subscriber terminals, and therefore it is difficult to control the sleep mode in the IEEE 802.16e communication system.
FIG. 1 is a flowchart illustrating a conventional sleep mode controlling method proposed by the IEEE 802.16e communication system. Typically, controlling a sleep mode of the IEEE 802.16e communication system begins with either a subscriber terminal request or by control of a base station. Herein, FIG. 1 illustrates a sleep mode controlling method which is started by a subscriber terminal request.
Referring to FIG. 1, a subscriber terminal 10, which desires to enter a sleep mode, sends a sleep request message (hereinafter, referred to as an SLP-REQ message) to a base station 20 (S31). The subscriber terminal 10 sends a minimum size value (e.g. a min-window) and a maximum size value (e.g. a max-window) of a sleep interval window according to its configuration, and a value of a listening interval, that is, a time interval during which the corresponding terminal awakes and determines if a message has become received. The unit of these values is a frame.
Next, the base station 20 having received the SLP-REQ message performs a sleep time scheduling with reference to preset sleep control information (e.g. the min-window, the max-window, and the listening interval which are allowable) (S32), and then sends a sleep response message (hereinafter, referred to as an SLP-RSP message) to the subscriber terminal 10 (S33). This SLP-RSP message includes the number of frames (hereinafter, referred to as a start-time) which remain until the subscriber terminal 10 enters the sleep mode, and a min-window value, a max-window value and a listening interval value which are approved by the base station 20. The unit of these values is a frame.
The subscriber terminal 10 having received the SLP-RSP message enters the sleep mode at the start-time included in the SLP-RSP message (S34). The subscriber terminal 10 awakes from the sleep mode after the sleep interval passes, and checks whether or not there exist PDU data which it should receive from the base station 20. That is, if the sleep interval passes, the subscriber terminal 10 enters an awake mode (S35) and checks a traffic-indication message (hereinafter, referred to as a TRF-IND message) which is broadcast by the base station 20 during the listening interval (S36). The TRF-IND message is information which the base station 20 broadcasts to the subscriber terminal 10, and includes basic connection identification (CIDs) of a terminal to which PDU data should be transmitted.
The subscriber terminal 10 determines whether or not its own basic CIDs (BCIDs) are included in the TRF-IND message and then determines whether or not to awake form the sleep mode. That is, when the terminal's own BCIDs are included in the received TRF-IND message, the subscriber terminal 10 recognizes that there are PDU data to be received, and thus awakes from the sleep mode. If the TRF-IND message having been received by the subscriber terminal 10 is a positive traffic indication (S37), the subscriber terminal 10 is shifted to an active mode (S38).
In contrast, when the terminal's own BCIDs are not included in the received TRF-IND message, the subscriber terminal 10 determines that no PDU data exists to be transmitted to the subscriber terminal 10, and enters the sleep mode again. If the TRF-IND message having been received by the subscriber terminal 10 is a negative traffic indication, the subscriber terminal 10 is shifted to the sleep mode (S34) and then maintains the sleep mode during the sleep interval.
When the TRF-IND message is not the positive traffic indication in step S37, the subscriber terminal 10 increases the sleep interval by twice as long as the prior sleep interval (S39) and then maintains the sleep mode during the increased sleep interval. The subscriber terminal 10 repeats the sleep mode and the awake mode until it is shifted to the active mode, and increases the sleep interval by twice as long as the prior sleep interval every repetition period until the sleep interval comes into the max-window which the base station 20 permits. In this way, the IEEE 802.16e communication system drives the sleep mode while increasing the sleep interval by twice as long as the prior sleep interval by means of the above-mentioned sleep update algorithm. Accordingly, in the IEEE 802.16e communication system, a sleep interval becomes increased according to an exponential power of 2, which makes it difficult for a base station to manage each sleep interval of a plurality of subscriber terminals.
In the IEEE 802.16e communication system, three messages, that is, a SLP-REQ message, a SLP-RSP message, and a TRF-IND message, are defined between a subscriber terminal and a base station in order for the subscriber terminal to enter a sleep mode.
FIGS. 2a to 2d are views showing conventional message formats transceived between a base station and a subscriber terminal in order to control the sleep mode as described above. That is, FIG. 2a shows a format of a SLP-REQ message 40, FIG. 2b shows a format of a SLP-RSP message 50a used in denying a sleep mode, FIG. 2c shows a format of a SLP-RSP message 50b used in approving a sleep mode, and FIG. 2d shows a format of a TRF-IND message 60.
Referring to FIG. 2a, the SLP-REQ message 40 includes a management message type (8 bits) 41, a min-window (6 bits) 42, a max-window (10 bits) 43, and a listening interval (8 bits) 44. The SLP-REQ message 40 is a dedicated message transmitted on the basis of a connection ID (CID) of a subscriber terminal, representing a request of a sleep mode by the subscriber terminal.
Herein, the management message type 41 is information representing the message types that are currently being transmitted. For instance, when the management message type is ‘45’, it means that the corresponding message is an SLP-REQ message. The management message type 41 consists of 8 bits.
The min-window 42 represents a start value requested for the sleep interval (measured in frames), and the max-window 43 represents a stop value requested for the sleep interval (measured in frames). That is, the sleep interval is updated while being increased according to an exponential power of 2 of the min-window value within a range from the min-window value to the max-window value.
The listening interval 44 represents a requested listening interval (measured in frames).
Herein, all of the min-window 42, the max-window 43, and the listening interval 44 are set in the unit of a frame.
Referring to FIG. 2b, the SLP-RSP message 50a used in denying a sleep mode request includes a management message type (8 bits) 51a, a sleep-approved area (1 bit) 52a, and a reserved area (7 bits) 53a. This SLP-RSP message 50a is a dedicated message transmitted on the basis of the connection ID (CID) of the subscriber terminal, and is a message setting a sleep timing of a the subscriber terminal after scheduling of a sleep time of the subscriber terminal in a base station.
Herein, the management message type 51a is information representing the message types that are currently being transmitted. For instance, when the management message type is ‘46’, it means that the corresponding message is an SLP-RSP message.
The sleep-approved area 52a is expressed in 1 bit. When the sleep-approved area 52a is zero, the subscriber terminal cannot be shifted to the sleep mode. The reserved area 53a is an preparatory area.
Referring to FIG. 2c, the SLP-RSP message 50b, which is transmitted to a subscriber terminal when a base station approves a sleep request, includes a management message type (8 bits) 51b, a sleep-approved area (1 bit) 52b, a start-time (7 bits) 53b, a min-window 54b, a max-window 55b and a listening interval 56b. 
The management message type 51b is information representing the message types that are currently being transmitted. For instance, when the management message type is ‘46’, it means that the corresponding message is an SLP-RSP message.
The sleep-approved area 52b is expressed in 1 bit. When the sleep-approved 52b is ‘1’, the sleep-mode request is approved.
The start-time 53b represents values of frames required until the subscriber terminal enters a first sleep interval, from which a frame having received the SLP-RSP message is excluded. The subscriber terminal is state-transited into the sleep mode after passing through frames from a frame positioned next to a frame receiving the sleep mode response message to frames corresponding to the start time.
The min-window 54b represents a start value for the sleep interval (measured in frames), the max-window 55b represents a stop value for the sleep interval (measured in frames), and the listening interval 56b represents a value for a listening interval (measured in frames).
Referring to FIG. 2d, the TRF-IND message 60 includes a management message type (8 bits) 61, the number of positive subscribers (NUM-POSITIVE) (8 bits) 62 and connection Ids CIDs of the respective positive subscribers (16 bits) 63 and 64. Differently from the SLP-REQ message and the SLP-RSP message, the TRF-IND message 60 is transmitted in a broadcasting method.
First, the management message type 61 is information representing the message types that are currently being transmitted. For instance, when the management message type 61 is ‘47’, it means that the corresponding message is a TRF-IND message.
The number of positive subscribers 62 represents the number of subscriber terminals to which packet data will be transmitted, and the connection IDs of the respective positive subscriber 63 and 64 include connection identification information the number of which corresponds to the number of the positive subscribers.
FIG. 3 is a diagram for explaining a conventional sleep interval update algorithm proposed by the IEEE 802.16e communication system. In FIG. 3, a reference mark ‘SS’ represents a subscriber terminal, a reference mark ‘BS’ represents a base station, and a box in which the ‘SS’ and ‘BS’ are written represents a frame.
FIG. 3 shows that the subscriber terminal SS requests a sleep mode to the base station BS at Nth frame (S71), and repeats a sleep interval and a listening interval when the base station BS responds to the sleep request by designating a sleep mode start time as (N+3)th frame at (N+1)th frame (S72). The initial sleep interval consists of two frames, but the second sleep interval consists of four frames corresponding to twice as many as the initial sleep interval.
In the typical IEEE 802.16e communication system as described above, since subscriber terminals request a sleep mode at different time points and sleep intervals of the subscriber terminals become increased according to an exponential power of 2, it is difficult for a base station to manage the sleep intervals of the subscriber terminals. Further, it is difficult to manage the subscriber terminals in a group unit.